In a conventional CMOS image sensor, an integrated circuit contains an array of pixel sensors, or “pixels,” each pixel including a photodetector that develops an analog voltage change proportional to a number of photons striking the detector during an exposure interval. At the conclusion of the exposure interval, a voltage developed on the photodetector is typically amplified and delivered to an analog-to-digital converter (ADC), which digitizes the amplified voltage.
Pixel geometries have scaled downward as CMOS processing has improved, resulting in performance rivaling that of larger and more power-consumptive Charge Coupled Devices (CCD), which have been widely applied in imaging devices such as digital single lens reflex (DSLR) cameras and camcorders. CMOS devices, having lower cost and performance equivalent to CCDs, now enjoy widespread adoption in modern imaging devices including smart phones, web cameras, and DSLR cameras. Despite the widespread adoption of CMOS imaging sensors however, limitations in performance exist due to various noise sources and dynamic range constraints.